Makar Sankranti (also known as Makara Sankranti or Maghi) refers both to a specific solar day in the Hindu calendar and a Hindu festival in worship to deity Surya (sun) that is observed in January every year. It marks the first day of sun's transit into the Makara (Capricorn), marking the end of the month with the winter solstice and the start of longer days.

Makar Sankranti is one of the few ancient Hindu festivals that has been observed according to solar cycles, while most festivals are set by the lunar cycle of the lunisolar Hindu calendar. Being a festival that celebrates the solar cycle, it approximately always falls on the same Gregorian date every year (January 14), except in rare years when the date shifts by a day for that year, because of the difficulty of earth-sun relative movement. The festivities connected with Makar Sankranti are known by various names such as Lohri by North Indian Hindus and Sikhs, Sukarat in central India, Bhogali Bihu by Assamese Hindus, and Pongal by Tamil and other South Indian Hindus.source:https://en.wikipedia.org/